Cobalt-based nanoparticles prepared from MOF-carbon templates as efficient hydrogenation catalysts

Article abstract of DOI:10.1039/c8sc02807a

The development of efficient and selective nanostructured catalysts for industrially relevant hydrogenation reactions continues to be an actual goal of chemical research. In particular, the hydrogenation of nitriles and nitroarenes is of importance for the production of primary amines, which constitute essential feedstocks and key intermediates for advanced chemicals, life science molecules and materials. Herein, we report the preparation of graphene shell encapsulated Co₃O₄- and Co-nanoparticles supported on carbon by the template synthesis of cobalt-terephthalic acid MOF on carbon and subsequent pyrolysis. The resulting nanoparticles create stable and reusable catalysts for selective hydrogenation of functionalized and structurally diverse aromatic, heterocyclic and aliphatic nitriles, and as well as nitro compounds to primary amines (>65 examples). The synthetic and practical utility of this novel non-noble metal-based hydrogenation protocol is demonstrated by upscaling several reactions to multigram-scale and recycling of the catalyst.

Full text of DOI:10.1039/c8sc02807a

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Cobalt-based nanoparticles prepared from MOF–
carbon templates as efficient hydrogenation
catalysts†
Cite this: DOI: 10.1039/c8sc02807a
All publication charges for this article
have been paid for by the Royal Society
of Chemistry
a
ab
Kathiravan Murugesan,
Thirusangumurugan Senthamarai,a Manzar Sohail,
Ahmad S. Alshammari,c Marga-Martina Pohl,a Matthias Beller
a
*
a
*
and Rajenahally V. Jagadeesh
The development of efficient and selective nanostructured catalysts for industrially relevant hydrogenation
reactions continues to be an actual goal of chemical research. In particular, the hydrogenation of nitriles and
nitroarenes is of importance for the production of primary amines, which constitute essential feedstocks
and key intermediates for advanced chemicals, life science molecules and materials. Herein, we report
the preparation of graphene shell encapsulated Co3O4- and Co-nanoparticles supported on carbon by
the template synthesis of cobalt-terephthalic acid MOF on carbon and subsequent pyrolysis. The
resulting nanoparticles create stable and reusable catalysts for selective hydrogenation of functionalized
and structurally diverse aromatic, heterocyclic and aliphatic nitriles, and as well as nitro compounds to
primary amines (>65 examples). The synthetic and practical utility of this novel non-noble metal-based
hydrogenation protocol is demonstrated by upscaling several reactions to multigram-scale and recycling
of the catalyst.
Received 26th June 2018
Accepted 8th September 2018
DOI: 10.1039/c8sc02807a
rsc.li/chemical-science
literally thousands of such catalytic materials, the majority of
them does not permit for the renement of functionalized and
complex molecules.19–25 However in recent years, more potent
Introduction
The development of base metal catalysts for sustainable and
cost-effective processes is an actual and long standing goal of
chemical research in academia and industry.1–3 Among the
different synthetic technologies, catalytic hydrogenations
represent a versatile tool box for the preparation of numerous
ne and bulk chemicals, fuels, and life science molecules.4–10
Until today, on a practical scale these reactions mainly rely on
precious metal-based catalysts,4–9 as well as RANEY® nickel.4–10
However, the availability and high price of precious metals, and
selectivity problems and sensitivity of RANEY® Ni spurred
interest towards alternative catalysts.1–3,11–18 In this respect,
reusable supported nanoparticles are attractive due to easy
separation, accessibility of active sites, control of size, and
prospect of mild reaction conditions.15–25 Traditionally, sup-
ported metal nanoparticles are prepared by thermal (pyrolysis
or calcination) or chemical reduction of the respective metal
salts on heterogeneous supports.19–25 Despite the synthesis of
materials were prepared by using specic precursors such as
metal–nitrogen complexes15–17,26 or structure-controlling
templates.27–35 In this respect, metal organic frameworks
(MOFs) built from metal ions and different organic linkers can
be assembled in a highly exible manner.20–27 So far, MOFs
proved to be suitable for gas separation and storage, but also
interesting catalytic applications have been realized,27–30 espe-
cially via subsequent pyrolysis processes.31–34 Complementary to
these materials, most recently we described the use of cobalt-
diamine-dicarboxylic acid-based MOFs as precursors for the
preparation of supported nanoparticles and single Co atoms,
which exhibit excellent catalytic activity for reductive amina-
tions.35 In this case, both the nitrogen and carboxylic acid linker
was necessary to produce an active material. In continuation of
our efforts to develop cost-efficient materials36 for sustainable
catalysis, herein we describe the expedient preparation of
a cobalt-terephthalic acid MOF–carbon template, which forms
aer pyrolysis graphene shell encapsulated Co3O4/Co particles.
The resulting nanoparticles are supported on carbon, which
creates stable and reusable catalysts for selective hydrogena-
tions of aliphatic and aromatic nitriles and nitro compounds
(Fig. 1).
a
¨
¨
Leibniz-Institut fur Katalyse e. V. an der Universitat Rostock, Albert-Einstein-Str. 29a,
18059 Rostock, Germany. E-mail: Matthias.Beller@catalysis.de; Jagadeesh.
Rajenahally@catalysis.de
bThe Center of Research Excellence in Nanotechnology (CENT), King Fahd University of
Petroleum and Minerals, Dhahran 31261, Saudi Arabia
The resulting amines are of interest to chemistry, medicine,
biology, biochemistry and material science.37–43 For example,
amine motifs constitute an integral part of the majority of life
cKing Abdulaziz City for Science and Technology, Riyadh 11442, Saudi Arabia
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c8sc02807a
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Table 1 Hydrogenation of benzonitrile to benzylamine: activity of
cobalt catalystsa
Entry Catalyst
Conv. (%) Yield (%)
1b
2c
3c
4c
5c
6d
7d
8e
Cobalt-terephthalic acid MOF@C-800 >99 <15
Cobalt-terephthalic acid MOF@C-800 >99
97
<2
<1
<1
<1
<1
96
Cobalt nitrate@C-800
<5
<2
<2
<2
<2
Cobalt-terephthalic acid MOF@C
Cobalt-terephthalic acid MOF
Cobalt nitrate + terephthalic acid
Co(NO3)2$6H2O
Fig.
1 Preparation of graphene encapsulated cobalt oxide- and
cobalt-nanoparticles supported on carbon by the pyrolysis of cobalt-
terephthalic acid MOF–carbon template.
Cobalt-terephthalic acid MOF-800
>99
a
Materials are pyrolyzed at 800 ꢀC for 2 h under argon. Cobalt content
b
science molecules and natural products.37–43 In fact, among 200
existing drugs, more than 170 contain at least one nitrogen
atom regulating their activities.37 Among the different kinds of
amines, primary amines attract special interest because they
can be easily further transformed; thus constitute central
intermediates for the production of specialty chemicals, phar-
maceuticals, agrochemicals, dyes and polymers. In industry
primary benzylic, aliphatic and aromatic amines are oen
prepared by the hydrogenation of the corresponding nitriles44–46
and nitroarenes,15,16,47–53 respectively. Apart from traditional
noble metal-catalysts,44–46 Raney®-nickel54–57 or -cobalt,57 Fe,58,59
Co,60–64 and Mn65-based catalysts have recently been disclosed.
Despite these achievements, still the development of active and
selective nanocatalysts based on earth abundant metals is
desired.
in the pyrolyzed sample supported on carbon ¼ 4.5 wt%. Reaction
conditions: Heterogeneous catalysis conditions
¼
0.5 mmol
benzonitrile, 25 mg catalyst (3.8 mol% Co), 3 mL toluene, 25 bar H2,
c
d
120 ꢀC, 15 h. Same as ‘a’ with 5 bar NH3. Homogeneous catalysis
conditions
¼
0.5 mmol benzonitrile, 0.02 mmol Co(NO3)2$H2O,
0.06 mmol linker, 3 mL toluene, 25 bar H2, 5 bar NH3, 120 ꢀC, 15 h.
e
Material was prepared by the direct pyrolysis (800 ꢀC, 2 h Ar) of MOF
without carbon support.
support and tested for its catalytic activity. Interestingly, this
material was also found to be active and produced 96% of
benzylamine (Table 1, entry 8). However, due to the high cobalt
content (40% wt%), this catalyst (cobalt-terephthalic acid MOF-
800) exhibits less stability compared to the cobalt-terephthalic
acid MOF@C-800.
To further optimize the benchmark reaction and to study the
course of the formation of products, we varied different
parameters such as ammonia concentration, reaction time,
amount of catalyst, and hydrogen pressure in the presence of
the optimal catalyst (cobalt-terephthalic acid MOF@C-800). As
shown in Fig. S2,† complete conversion of benzonitrile (0.5
mmol-scale) and formation of benzylamine as the sole desired
product was observed in presence of 20 mg of catalyst at 20 bar
of H2.
Results and discussion
Catalyst preparation and activity studies
At the start of our investigations, we prepared a cobalt-
terephthalic acid MOF template on carbon by reacting cobalt
nitrate and terephthalic acid (1 : 3) in DMF with carbon powder
at 150 ꢀC. Aer slow evaporation of solvent, the corresponding
material was pyrolyzed at different temperatures (400, 600, 800,
and 1000 ꢀC) under inert atmosphere. The activity of the
prepared potential catalysts was tested for the hydrogenation of
benzonitrile to benzylamine as a bench mark reaction. Among
these, cobalt-terephthalic acid MOF@C-800 was the most active
material. However, a mixture of the desired benzylamine (<15%)
and several side products such as N-benzylidenebenzylamine
and dibenzylamine were observed (Table 1, entry 1). To
suppress their formation, the reaction was performed in pres-
ence of hydrogen and ammonia. The latter is known to control
the selective formation of primary amines from nitriles
(Fig. S1†). Advantageously, under these conditions benzylamine
was obtained in 97% yield (Table 1, entry 2). Other materials
such as pyrolyzed cobalt nitrate on carbon (cobalt nitrate@C-
800), unpyrolyzed MOF–carbon template (cobalt-terephthalic
acid MOF@C) and isolated MOF (cobalt-terephthalic acid
MOF) were also tested and none of these materials were active
(Table 1, entries 3–5). As expected, cobalt nitrate and cobalt-
terephthalic acid under homogeneous reaction conditions
were also not active (Table 1, entries 6–7). Further, the cobalt-
Characterization of the active nano-catalyst
In order to understand the structural features of the most active
material, cobalt-terephthalic acid MOF@C-800 was character-
ized using Cs-corrected STEM (scanning transmission electron
microscopy), XRD (X-ray diffraction), EPR (electron para-
magnetic resonance), and XPS (X-ray photoelectron spectros-
copy) spectral analysis. TEM analysis of the active material
Fig. 2 TEM images of cobalt-terephthalic acid MOF@C-800 catalyst
showing Co3O4 and Co-nanoparticles (A) and metallic cobalt particles
terephthalic acid MOF was pyrolyzed directly without carbon encapsulated in graphene shells (B and C).
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revealed the formation of cobalt oxide (Co3O4) particles with 5–
30 nm size (Fig. 2). In addition, the material also contained
metallic cobalt nanoparticles. Interestingly, both types of
nanoparticles are encapsulated within graphene shells (Fig. 2).
In contrast, the inactive material cobalt nitrate@C-800 con-
tained hollow Co3O4 particles above 50 nm size (Fig. S4†).
Notably, this material contained no graphene shells. Further,
the formation of Co3O4-particles was conrmed by XRD data
(Fig. S7†). Also, XRD analysis revealed the formation of cobalt-
terephthalic acid MOF (Fig. S8†).
To understand the nature of the active metal species in more
detail, EPR measurements were performed, too. Cobalt-
terephthalic acid MOF@C-800 displayed a broad signal with
a resonance peak observed at 3391 G with full width at half
maximum (FWHM) 1640 G (Fig. S9†). The g value 2.572
observed was about 23% higher than the g value of free electron
(2.00) in space. This indicates Co in higher oxidation states
(Co2+/Co3+). The observation of only one peak indicates the
presence of one paramagnetic species predominantly.66
Further, to conrm the presence of Co3O4, we performed XPS
analysis of Co2p and O1s electrons for cobalt-terephthalic acid
MOF@C-800 (Fig. S10†). The binding energy values of its most
intense Co2p signals match very closely to the presence of
Co3O4 at the surface of the catalyst. The Co2p3/2 and Co2p1/2
peaks appeared at 779.75 eV and 794.91 eV, respectively. The
Co2p3/2–Co2p1/2 splitting energy of 15.16 eV is also in close
agreement with the presence of Co3O4. Weak peaks, which are
the characteristics of Co2+ in Co3O4, support the absence of
other CoO species. It is generally known that in Co3O4, the
Co2p3/2 spectrum of cobalt oxide is representative for high spin
Co2+ and low spin Co3+ ions.67,68 The O1s surface spectra showed
a signicant broadening towards higher binding energy and
was deconvoluted in three components. The rst peak at
529.05 eV is representative of a cobalt oxide network, while the
second peak present at 531.60 eV could be related to the pres-
ence of hydroxyl groups in the inner surface. The third broad
peak at 535.23 eV is related to water adsorbed at the surface.69
The BET surface area of cobalt-terephthalic acid MOF@C-800 is
158.4 m2 gꢁ1 and the corresponding average pore size is
7.96 nm (Fig. S9 and S10†). Notably, TEM analysis revealed the
formation of both Co3O4 and metallic Co nanoparticles in the
most active sample (cobalt-terephthalic acid MOF@C-800).
However, XPS and XRD analyses detected only Co3O4-parti-
cles. This might be due to the small quantity or size of metallic
cobalt particles, which are difficult to detect by XRD or XPS.
Fig. 3 Cobalt-terephthalic acid MOF@C-800-catalyzed hydrogena-
tion of benzonitriles and cyano-heterocycles to primary aminesa.
aReaction conditions: 0.5 mmol benzonitrile, 25 mg catalyst (3.8 mol%
Co), 3 mL toluene, 25 bar H2, 5 bar NH3, 120 ꢀC, 16 h, isolated yields.
bGC yields using 100 mL n-hexadecane. Isolated as respective hydro-
chloride salts.
obtained in 85–95% yield without signicant dehalogenations
(Fig. 3; products 7–14). In order to apply this protocol for
advanced organic synthesis and drug discovery, achieving high
chemo-selectivity is of crucial importance. In this regard, we
were pleased to nd excellent hydrogenation selectivity in the
presence of amide, ester, and even C–C double and triple bonds
(Fig. 3; products 17–21). Furthermore, diverse heterocyclic
amines have been prepared from the corresponding nitriles
(Fig. 3; products 23–29).
Hydrogenation of functionalized (hetero)aromatic nitriles
With the optimal material (cobalt-terephthalic acid MOF@C-
800) in hand, we investigated the scope and general applica-
bility for the hydrogenation of nitriles. As shown in Fig. 3 and 4,
various functionalized and structurally diverse benzonitriles,
heterocyclic nitriles and challenging aliphatic ones smoothly
Hydrogenation of aliphatic nitriles
underwent hydrogenation to produce the corresponding Next, we performed the hydrogenation of aliphatic nitriles to
primary amines in good to excellent yields. For example, 8 the corresponding primary amines (Fig. 4). Compared to
different halogenated benzylic amines, which constitute aromatic nitriles, such hydrogenations are in general more
common building blocks in the chemical industry, were difficult and need harsher conditions. Fortunately, this catalyst
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Fig.
4 Hydrogenation of aliphatic nitriles catalyzed Co3O4/Co-
nanoparticles. aReaction conditions: 0.5 mmol benzonitrile, 25 mg
catalyst (3.8 mol% Co), 3 mL toluene, 25 bar H2, 5 bar NH3, 120 ꢀC, 16 h,
isolated yields. bGC yields using 100 mL n-hexadecane. Isolated as
respective hydrochloride salts.
is similar active and selective for the hydrogenation of aliphatic
substrates, too. As a result, aliphatic amines including long
chain, (bi)cyclic and as well as allylic ones were obtained in up
to 93% yield (Fig. 4). The preparation of hexamethylenediamine
in 75%—a central precursor for nylon 66 polymer (Fig. 4;
product 43)—highlights the industrial relevance of this
methodology.
Chemoselective hydrogenation of nitroarenes to anilines
Fig. 5 Cobalt-terephthalic acid MOF@C-800-catalyzed hydrogena-
tion of functionalized nitroarenes to anilinesa. aReaction conditions:
0.5 mmol nitroarene, 25 mg catalyst (3.8 mol% Co), 3 mL THF–H2O
(1 : 1), 20 bar H2, 120 ꢀC, 20 h, isolated yields. bGC yields using 100 mL
n-hexadecane. cWith 40 bar H2.
Aer having demonstrated the reduction of nitriles, we specu-
lated on the utility of our cobalt-catalyst for other hydrogena-
tions to give amines.
In this context, several nitroarenes were hydrogenated to
produce the corresponding anilines with excellent yields
(Fig. 5–6). Similar to nitriles, aromatic, heterocyclic and
aliphatic nitro compounds were selectively reduced. For
example, halogenated anilines were obtained in up to 95% yield
without dehalogenation (Fig. 5; products 48–54). Most inter-
compounds were successfully hydrogenated and produced
primary amines in 78 and 91% yield, respectively (Fig. 6;
products 76 and 77).
Demonstrating scale-up and catalyst recycling
estingly, 4-iodonitrobenzene, which is
a highly sensitive
compound, led in 95% to the corresponding aniline (Fig. 5;
product 53). In other structurally diverse and functionalized
molecules the nitro group was also selectively reduced. As
a result, hydroxyl groups, aldehyde, ketone, ester, amide, and
C–C double bonds were untouched.
To complement the synthetic viability of the catalyst system and
the developed protocols, upscaling of selected reactions and
Hydrogenation of nitro heterocycles and nitroalkanes
Next, 5 representative nitro-substituted heteroarenes were
hydrogenated to produce amino-substituted N-heterocycles
(Fig. 6; products 70–75). For example, the resulting 8-amino-
quinoline (product 71) represents a key intermediate for prep-
aration of primaquine, tafenoquine and pamaquine drugs,
which are used in the treatment of malaria. Finally, nitro-
cyclohexane and 1-nitrohexane were tested. It should be noted
that most of the known nitro reduction catalysts either show
poor reactivity or do not work at all for aliphatic nitro
Fig.
6 Hydrogenation of nitro-heterocycles and aliphatic nitro
compounds catalyzed cobalt-terephthalic acid MOF@C-800-catalyst.
aReaction conditions: 0.5 mmol nitro compound, 25 mg catalyst
(3.8 mol% Co), 3 mL THF–H2O (1 : 1), 20 bar H2, 120 ꢀC, 20 h, isolated
yields. bWith 40 bar H2 in 3 mL t-butanol solvent. cGC yields using 100
compounds. Favorably, using this novel cobalt catalyst both mL n-hexadecane.
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recycling of catalyst are presented. The hydrogenation of three
nitriles two nitroarenes on gram-scale (2–5 g) proceeded easily
and in all cases similar yields to mg-scale reactions were ob-
tained (Fig. 7).
In addition, these cobalt oxide nanoparticles proved to be
highly stable in the benchmark hydrogenation and were recy-
cled and reused for 5 times without signicant loss of catalytic
activity (Fig. 8). TEM analysis of the reused catalyst showed that
there is no change in the structure of metallic Co particles
(Fig. S5 and S6†). However, a change in the structure of the
cobalt oxide particles was observed. Some of these particles
migrate out from graphene shells and form new structures on
carbon support (Fig. S5 and S6†).
Fig.
8
Demonstrating the recycling of cobalt-terephthalic acid
MOF@C-800-catalyst for the hydrogenation of benzonitrile to ben-
zylamine. Reaction condition: 5 mmol benzonitrile, 250 mg catalyst,
(3.8 mol% Co), 20 mL toluene, 25 bar H2, 5 bar NH3, 120 ꢀC, 16 h, GC
yields using n-hexadecane standard.
Experimental
General considerations
XRD powder pattern were recorded either on a Panalytical
X'Pert diffractometer equipped with a Xcelerator detector or on
a Panalytical Empyrean diffractometer equipped with a PIXcel
3D detector system. Both were used with automatic divergence
slits and Cu ka1/a2 radiation (40 kV, 40 mA; l ¼ 0.015406 nm,
0.0154443 nm). Cu b-radiation was excluded by using nickel
lter foil. Peak positions and prole were tted with pseudo-
Voigt function using the HighScore Plus soware package
(Panalytical). Phase identication was done by using the PDF-2
database of the International Center of Diffraction Data (ICDD).
EPR spectra were recorded in X-band at 273 K on a Adani
Spinscan X-band electron paramagnetic resonance (EPR) spec-
trometer equipped with cavity Q factor and MW power
measurement with a magnetic eld modulation capability of
10–250 kHz. The data were measured at microwave frequency ¼
9.48 GHz; modulation amplitude ¼ 8 G; modulation frequency
¼ 100 kHz as reported in the reference.
All nitriles and nitroarenes were obtained commercially from
various chemical companies. Cobalt(II) nitrate hexahydrate,
terephthalic acid were obtained from Sigma-Aldrich. Dry
toluene, 99.8% was obtained from across chemicals. Carbon
powder, VULCAN® XC72R with Code XVC72R and CAS no.
1333-86-4 was obtained from Cabot Corporation Prod. The
pyrolysis experiments were carried out in Nytech-Qex oven.
Before using, the purity of nitriles and nitroarenes has been
checked.
The TEM measurements were performed at 200 kV with an
aberration-corrected JEM-ARM200F (JEOL, Corrector: CEOS).
The microscope is equipped with a JED-2300 (JEOL) energy-
dispersive X-ray-spectrometer (EDXS). The aberration cor-
rected STEM imaging (High-Angle Annular Dark Field (HAADF)
and Annular Bright Field (ABF) were performed under the
following conditions. HAADF and ABF both were done with
a spot size of approximately 0.1 nm, a convergence angle of 30–
36ꢀ and collection semi-angles for HAADF and ABF of 90–170
mrad and 11–22 mrad respectively. The solid samples were
deposed without any pretreatment on a holey carbon supported
Cu-grid (mesh 300) and transferred to the microscope.
XPS data was obtained with a VG ESCALAB220iXL (Thermo-
Scientic) with monochromatic Al Ka (1486.6 eV) radiation. The
electron binding energies EB were obtained without charge
compensation. For quantitative analysis the peaks were deconvo-
luted with Gaussian–Lorentzian curves, the peak area was divided
by a sensitivity factor obtained from the element specic Scoeld
factor and the transmission function of the spectrometer.
All catalytic experiments were carried out in 300 mL and
100 mL autoclaves (PARR Instrument Company). In order to
avoid unspecic reactions, all catalytic reactions were carried
out either in glass vials, which were placed inside the autoclave,
or glass/Teon vessel tted autoclaves.
GC and GC-MS were recorded on Agilent 6890N instrument.
GC conversion and yields were determined by GC-FID, HP6890
with FID detector, column HP530 m ꢂ 250 mm ꢂ 0.25 mm.
1H, 13C NMR data were recorded on a Bruker ARX 300 and
Bruker ARX 400 spectrometers using DMSO-d6, CD3OD and
CDCl3 solvents.
Fig.
7 Representing the practical utility of the cobalt-catalyzed
Procedure for the preparation of cobalt-terephthalic acid
hydrogenation protocol for gram scale reactions. Reaction conditions:
a3–5 g nitrile, 25 mg catalyst (3.8 mol% Co) for each for each 0.5 mmol MOFs–carbon template and graphene shell encapsulated
substrate, 25 bar H2, 5 bar NH3, 120 ꢀC, 20–60 mL toluene 16 h,
cobalt-based nanoparticles
Isolated respective hydrochloride salts. b2–3 g nitroarene 25 mg
catalyst (3.8 mol% Co) for each 0.5 mmol substrate, 40 bar H2, 120 ꢀC,
A 50 mL dried round bottomed ask was charged with magnetic
20–40 mL THF–H2O (1 : 1), 20 h, isolated yields.
stirring bar and 1.52 mmol of cobalt(II) nitrate hexahydrate and
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4.58 mmol of terephthalic acid. Then 25–30 mL of DMF was evaporation to remove solvent and ammonia. The crude
added and stirred at 140–150 ꢀC for 20–30 min. To this mixture, product was diluted with ether and 1–2 mL methanol HCl or
1.5 g of carbon powder (VULCAN® XC72R) was added followed dioxane HCl (1.5 M HCl in methanol or 4 N HCl in dioxane) was
by the addition of 15 mL DMF and the reaction mixture again added and stirred at room temperature for 4–5 h to obtain
was stirred at 150 ꢀC for 4–5 h by xing reux condenser. Then, hydrochloride salt of amine. Then, the solvent was removed and
the reux condenser and magnetic stirring bar were removed the resulted hydrochloride salt of amine is dried under high
and the round bottomed ask containing reaction products vacuum. For determining the yields using GC analysis, aer
were. Then, the round bottomed ask containing reaction completing the reaction n-hexadecane (100 mL) as standard was
mixture was placed into an aluminium block preheated at added to the reaction vials and the reaction products were
150 ꢀC and allowed to stand without stirring and closing for 20– diluted with ethyl acetate followed by ltration using plug of
22 h at 150 ꢀC in order to slow evaporation of DMF and to form silica and then analyzed by GC.
Co–MOF–carbon template via solvothermal process. Aer
complete drying, the material was cooled to room temperature
and grinded to ne powder. The powdered material was pyro-
lyzed at 800 ꢀC for 2 hours under an argon atmosphere and then
cooled to room temperature aer pyrolysis. (Elemental analysis
(wt%): cobalt-terephthalic acid MOF@C-800: Co ¼ 4.5, C ¼
90.70%, H ¼ 0.25%.
General procedure for the hydrogenation of nitro compounds
The magnetic stirring bar and corresponding nitro compound
(0.5 mmol) were transferred to the glass vial and then 3 mL
solvent (water–THF or tertiary butanol) was added. Then, 25 mg
of catalyst was added and the vial was tted with septum, cap
and needle. The reaction vials (8 reaction vials at a time in case
of 0.5 mmol scale) were placed into a 300 mL autoclave. The
autoclave was ushed with hydrogen twice at 30 bar pressure
and then it was pressurized to 20 bar or 40 bar hydrogen pres-
Procedure for the preparation and isolation of cobalt-
terephthalic acid MOFs
A 50 mL dried round bottomed ask was charged with magnetic sure. The autoclave was placed into an aluminium block (placed
stirring bar, 0.52 mmol of cobalt(II) nitrate hexahydrate and 30 minutes before counting the reaction time in ordered to
ꢀ
4.58 mmol of terephthalic acid. Then 25–30 mL of DMF was attain reaction temperature) preheated at 130 C and the reac-
added and stirred at 140–150 ꢀC for 20–30 min. Then, the round tions were stirred for required time. During the reaction the
bottomed ask containing reaction mixture was placed into an inside temperature of the autoclave was measured to be 120 ꢀC
aluminium block preheated at 150 ꢀC and stirred for 20–30 and this temperature was used as the reaction temperature.
minutes by xing reux condenser. Then, the reux condenser Aer the completion of the reaction, the autoclave was cooled to
and magnetic stirring bar were removed and the round room temperature. The remaining hydrogen was discharged
bottomed ask containing reaction products were allowed to and the samples were removed from the autoclave. Catalyst
stand without stirring and closing for 20–24 h at 150 ꢀC in order from the reaction mixture was ltered off and washed with THF
to slow evaporation of DMF and to form Co–MOFs via sol- and then ethyl acetate. The solvent form ltrate containing
vothermal process. Aerward the product obtained was cooled reaction product was removed in vacuo. The corresponding
down to room temperature and washed with hot DMF and then aniline was puried by column chromatography (silica; n-
dried at 150 ꢀC and at high vacuum.
hexane-ethyl acetate mixture). Then, dried over anhydrous
Na2SO4 and the solvent was removed in vacuo. For determining
the yields using GC analysis, aer completing the reaction n-
hexadecane (100 mL) as standard was added to the reaction vials
and the reaction products were diluted with THF followed by
ltration using plug of silica and then analyzed by GC.
General procedure for the hydrogenation of nitriles
The magnetic stirring bar and 0.5 mmol corresponding nitrile
compound was transferred to 8 mL glass vial and then 3 mL
solvent (toluene) was added. Then, 25 mg of catalyst was added
and the vial was tted with septum, cap and needle. The reac-
tion vials (8 vials with different substrates at a time) were placed
into a 300 mL autoclave. The autoclave was ushed with
Procedure for up-scaling the reactions
For the hydrogenation of nitriles. To a Teon or glass tted
hydrogen twice at 25 bar pressure and then it was pressurized 300 mL or 1.0 L autoclave, the magnetic stirring bar and cor-
with 5 bar ammonia gas and 25 bar hydrogen. The autoclave responding nitriles were transferred and then 120–150 mL of
was placed into an aluminium block preheated at 130 ꢀC dry toluene was added. Then aer, required amount of catalyst
(placed 30 minutes before counting the reaction time in ordered (25 mg for each 0.5 mmol substrate) was added. The autoclave
to attain reaction temperature) and the reactions were stirred was ushed with hydrogen twice at 30 bar pressure and then it
for required time. During the reaction the inside temperature of was pressurized with 5 bar ammonia gas and 25 bar hydrogen.
ꢀ
the autoclave was measured to be 120 C and this temperature The autoclave was placed into an aluminium block preheated at
was used as the reaction temperature. Aer the completion of 130 ꢀC (placed 30 minutes before counting the reaction time in
the reactions, the autoclave was cooled to room temperature. ordered to attain reaction temperature) and the reaction was
The remaining ammonia and hydrogen were discharged and stirred for required time. During the reaction the inside
the vials containing reaction products were removed from the temperature of the autoclave was measured to be 120 ꢀC and
autoclave. The catalyst was ltered off and washed with ethyl this temperature was used as the reaction temperature. Aer the
acetate. The ltrate containing product was subjected to completion of the reaction, the autoclave was cooled to room
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temperature. The remaining ammonia and hydrogen were dis- nitro compounds. The synthetic utility and practicability of this
charged and the reaction products were removed from the cobalt-based hydrogenation protocol was further established by
autoclave. The solid catalyst was ltered off and washed thor- performing gram-scale synthesis and recycling of the catalyst.
oughly with ethyl acetate. The reaction products were analyzed
by GC-MS and the corresponding primary amines were con-
verted to their respective hydrochloride salt and characterized.
Conflicts of interest
For the hydrogenation of nitroarenes. To a Teon or glass There are no conicts to declare.
tted 300 mL or 1.0 L autoclave, the magnetic stirring bar and
corresponding nitrocompounds were transferred and then 120–
150 mL of THF–H2O was added. Then aer, required amount of
Acknowledgements
catalyst (25 mg for each 0.5 mmol substrate) was added. The We gratefully acknowledge the support of the European Research
autoclave was ushed with hydrogen twice at 30 bar pressure Council (ERC), the State of Mecklenburg-Vorpommern, and King
and 40 bar hydrogen. The autoclave was placed into an Abdulaziz City for Science and Technology (KACST). We thank
aluminium block preheated at 130 ꢀC (placed 30 minutes before Wolfgang Baumann and his colleagues (LIKAT) for the charac-
counting the reaction time in ordered to attain reaction terization of the organic products.
temperature) and the reaction was stirred for required time.
During the reaction the inside temperature of the autoclave was
measured to be 120 C and this temperature was used as the
Notes and references
ꢀ
reaction temperature. Aer the completion of the reaction, the
autoclave was cooled to room temperature. The remaining
hydrogen was discharged and the reaction products were
removed from the autoclave. The solid catalyst was ltered off
and washed thoroughly with ethyl acetate. The reaction prod-
ucts were analyzed by GC-MS and the corresponding anilines
were isolated.
1 J. Maes, E. A. Mitchell and B. U. W. Maes, Base metals in
catalysis: From zero to hero in green and sustainable medicinal
chemistry: Methods, tools and strategies for the 21st century
pharmaceutical industry, L. Summerton, H. F. Sneddon, L. C.
Jones and J. H. Clark, Royal Society of Chemistry, 2016.
2 Chem 21, Base metal catalysis, http://learning.chem21.eu/
media/pdf/27/base-metal-catalysis-a4.pdf.
3 P. J. Chirik and R. Morris, Acc. Chem. Res., 2015, 48, 2495.
4 P. N. Rylander, Hydrogenation methods (best synthetic
methods), Academic Press, 1990; P. N. Rylander, Catalytic
hydrogenation in organic syntheses, Academic Press, 1979;
P. N. Rylander, Catalytic hydrogenation over platinum
metals, Academic Press, 2012.
5 S. Nishimura, Handbook of heterogeneous catalytic
hydrogenation for organic synthesis, Wiley, New York, 2001.
6 K. R. Westerterp and K. B. van Gelder, Stud. Surf. Sci. Catal.,
1997, 108, 47–67.
Procedure for catalyst recycling
The magnetic stirring bar and 5 mmol benzonitrile were
transferred to glass tted 100 mL autoclave and then 20 mL dry
toluene was added. Then aer, 250 mg of catalyst was added.
The autoclave was ushed with 30 bar hydrogen and then it was
pressurized with 5 bar ammonia gas and 25 bar hydrogen. The
autoclave was placed into heating system and reactions were
allowed to progress at 120 ꢀC (temperature inside the autoclave)
by stirring for required time. Aer the completion of the reac-
tion, the autoclave was cooled and the remaining ammonia and
hydrogen were discharged. To the reaction products, 250 mL n-
hexadecane as standard was added. The catalyst was then
separated by centrifugation and the centrifugate containing
reaction products was subjected to GC analysis for determining
the yield of benzyl amine. The separated catalyst by centrifu-
gation was then washed with ethyl acetate, dried under vacuum
and used without further purication or reactivation for the
next run.
7 J. Pritchard, G. A. Filonenko, R. van Putten, E. J. M. Hensen
and E. A. Pidko, Chem. Soc. Rev., 2015, 44, 3808–3833.
´
8 I. Karame, Hydrogenation, InTech, 2012.
9 H.-U. Blaser, C. Malan, B. Pugin, F. Spindler, H. Steiner and
M. Studer, Adv. Synth., 2003, 345, 103–151.
10 S. H. Tucker, J. Chem. Educ., 1950, 27, 489.
11 For price of metals, see: http://www.metalprices.com/.
12 A. Extance, Base metal catalysts strike hydrogenation gold,
chemistry
world,
http://kuchem.kyoto-u.ac.jp/chembio/
theme1.pdf.
13 R. M. Bullock, Science, 2013, 342, 1054–1055.
14 S. Borman, Catalysts that are less precious, Chem. Eng. News,
2013, 91, 27.
Conclusions
In conclusion, we prepared cobalt nanoparticles encapsulated 15 R. V. Jagadeesh, A.-E. Surkus, H. Junge, M.-M. Pohl,
¨
J. Radnik, J. Rabeah, H. Huan, V. Schunemann,
in graphene shells supported on carbon by pyrolysis of simple
cobalt salts and terephthalic acid (TPA). Compared to other
¨
A. Bruckner and M. Beller, Science, 2013, 342, 1073–1076.
¨
recently developed nano-catalysts, this Co–TPA–carbon catalyst 16 F. A. Westerhaus, R. V. Jagadeesh, G. Wienhofer, M.-M. Pohl,
does not require nitrogen-doping for activity, which opens new
avenues for catalyst design. The presented material constitutes
a general base-metal hydrogenation catalyst, which allows for
J. Radnik, A.-E. Surkus, J. Rabeah, K. Junge, H. Junge,
¨
M. Nielsen, A. Bruckner and M. Beller, Nat. Chem., 2013, 5,
537–543.
selective reduction of a series of functionalized and structurally 17 R. V. Jagadeesh, T. Stemler, A. E. Surkus, H. Junge, K. Junge
diverse aromatic, heterocyclic and aliphatic nitriles, as well as
and M. Beller, Nat. Protoc., 2015, 10, 548–557.
This journal is © The Royal Society of Chemistry 2018
Chem. Sci.

View Article Online
Chemical Science
Edge Article
18 E. de Smit and B. M. Weckhuysen, Chem. Soc. Rev., 2008, 37, 42 T. Yan, B. L. Feringa and K. Barta, Nat. Commun., 2014, 5,
2758–2781. 5602.
19 L. Filipponi and D. Sutherland, Nanotechnologies: Principles, 43 J. Maes, T. R. M. Rauws and B. U. W. Maes, Chem.–Eur. J.,
applications, implications and hands-on activities, European
Commission, European Union, 2012.
2013, 19, 9137–9141.
44 D. B. Bagal and B. M. Bhanage, Adv. Synth. Catal., 2015, 357,
20 V. Polshettiwar and T. Asefa, Nanocatalysis: Synthesis and
Applications, Wiley, 2013.
883–900.
45 S. Werkmeister, K. Junge and M. Beller, Org. Process Res.
21 P. Serp and K. Philippot, Nanomaterials in Catalysis, Wiley,
2012.
Dev., 2014, 18, 289–302.
46 C. de Bellefon and P. Fouilloux, Catal. Rev., 1994, 36, 459–
22 M. Sankar, N. Dimitratos, P. J. Miedziak, P. P. Wells,
506.
C. J. Kiely and G. J. Hutchings, Chem. Soc. Rev., 2012, 41, 47 H.-U. Blaser, H. Steiner and M. Studer, Chem. Cat. Chem.,
8099–8139. 2009, 1, 210–221.
23 J. Zecevic, G. Vanbutsele, K. P. de Jong and J. A. Martens, 48 M. Orlandi, D. Brenna, R. Harms, S. Jost and M. Benaglia,
Nature, 2015, 528, 245–248. Org. Process Res. Dev., 2018, 22, 430–445.
24 P. Munnik, P. E. de Jongh and K. P. de Jong, Chem. Rev., 49 A. Corma and P. Serna, Science, 2006, 313, 332–334.
ˇ
´
2015, 115, 6687–6718.
25 E. M. van Schrojenstein Lantman, T. Deckert-Gaudig,
50 T. Schwob and R. Kempe, Angew.Chem. Int .Ed., 2016, 55,
15175–15179.
A. J. G. Mank, V. Deckert and B. M. Weckhuysen, Nat. 51 D. Formenti, F. Ferretti, C. Topf, A.-E. Surkus, M.-M. Pohl,
Nanotechnol., 2012, 7, 583–586.
26 L. He, F. Weniger, H. Neumann and M. Beller, Angew. Chem.
Int. Ed., 2016, 55, 12582–12594.
27 H. Furukawa, K. E. Cordova, M. O'Keeffe and O. M. Yaghi,
Science, 2013, 341, 1230444.
J. Radnik, M. Schneider, K. Junge and M. Beller, J. Catal.,
2017, 351, 79–89.
52 B. Sahoo, D. Formenti, C. Topf, S. Bachmann, M. Scalone,
K. Junge and M. Beller, ChemSusChem, 2017, 10, 3035–3039.
53 P. Zhou, L. Jiang, F. Wang, K. Deng, K. Lv and Z. Zhang, Sci.
Adv., 2017, 3, e1601945.
´
´
28 A. Corma, H. Garcıa and F. X. Llabres i Xamena, Chem. Rev.,
2010, 110, 4606–4655.
54 W. Huber, J. Am. Chem. Soc., 1944, 66, 876–879.
29 H. Wang, Q.-L. Zhu, R. Zou and Q. Xu, Chem, 2017, 2, 52–80. 55 R. Novi, Hydrogenation of aliphatic nitriles over nickel catalysts
¨
30 L. Zhu, X.-Q. Liu, H.-J. Jiang and L.-B. Sun, Chem. Rev., 2017,
117, 8129–8176.
modied by formaldehyde, PhD thesis, ETH Zurich,
Switzerland, 2004, DOI: 10.3929/ethz-a-004877494.
31 P. Pachfule, D. Shinde, M. Majumder and Q. Xu, Nat. Chem., 56 P. Kukula, M. Studer and H.-U. Blaser, Adv. Synth. Catal.,
2016, 8, 718–724.
2004, 346, 1487–1493.
32 J. Tang and Y. Yamauchi, Nat. Chem., 2016, 8, 638–639.
57 R. J. Allain and G. D. Smith, US Pat., 4375003A, 1983.
33 W. Xia, A. Mahmood, R. Zou and Q. Xu, Energy Environ. Sci., 58 C. Bornschein, S. Werkmeister, B. Wendt, H. Jiao,
2015, 8, 1837–1866.
E. Alberico, W. Baumann, H. Junge, K. Junge and
34 (a) K. Shen, X. Chen, J. Chen and Y. Li, ACS Catal., 2016, 6,
M. Beller, Nat. Commun., 2014, 5, 4111.
5887–5903; (b) X. Wang and Y. Li, J. Mol. Catal. A: Chem., 59 S. Chakraborty, G. Leitus and D. Milstein, Chem. Comm.,
2016, 420, 56–65; (c) J. Long, K. Shen and Y. Li, ACS Catal.,
2017, 7, 275–284.
35 R. V. Jagadeesh, K. Murugesan, A. S. Alshammari,
2016, 52, 1812–1815.
60 S. Mukherjee, D. Srimani, S. Chakraborty, Y. Ben-David and
D. Milstein, J. Am. Chem. Soc., 2015, 137, 8888–8891.
H. Neumann, M.-M. Pohl, J. Radnik and M. Beller, Science, 61 P. Ji, K. Manna, Z. Lin, X. Feng, A. Urban, Y. Song and W. Lin,
2017, 358, 326–332. J. Am. Chem. Soc., 2017, 139, 7004–7011.
36 The applied linker, terephthalic acid (TPA) belongs to the 62 F. Chen, C. Topf, J. Radnik, C. Kreyenschulte, H. Lund,
most available carboxylic acids; see for example:
H. Schneider, A.-E. Surkus, L. He, K. Junge and M. Beller,
R. J. Sheehan, Terephthalic Acid, Dimethyl Terephthalate,
J. Am. Chem. Soc., 2016, 138, 8781–8788.
and Isophthalic Acid, Ullmann's Encyclopedia of Industrial 63 W. A. Butte and W. J. Murtaugh, US Pat., 4186146A, 1980.
Chemistry, Wiley-VCH, Weinheim, 2011.
37 S. A. Lawrence, Amines: synthesis, properties and applications,
Cambridge University Press, 2004.
38 A. Ricci, Amino group chemistry: from synthesis to the life
sciences, Wiley-VCH, 2008.
64 K. Tokmic, B. J. Jackson, A. Salazar, T. J. Woods and
A. R. Fout, J. Am. Chem. Soc., 2017, 139, 13554–13561.
65 S. Elangovan, C. Topf, S. Fischer, H. Jiao, A. Spannenberg,
W. Baumann, R. Ludwig, K. Junge and M. Beller, J. Am.
Chem. Soc., 2016, 138, 8809–8814.
39 http://njardarson.lab.arizona.edu/sites/njardarson.lab.
arizona.edu/les/Top200PharmaceuticalProductsRetail
Sales2015LowRes.pdf.
66 J. G. McAlpin, Y. Surendranath, M. Dincǎ, T. A. Stich,
S. A. Stoian, W. H. Casey, D. G. Nocera and R. D. Britt, J.
Am. Chem. Soc., 2010, 132, 6882–6883.
40 S. D. Roughley and A. M. Jordan, J. Med. Chem., 2011, 54, 67 N. S. McIntyre, D. D. Johnston, L. L. Coatsworth, R. D. Davidson
3451–3479. and J. R. Brown, Surf. Interface Anal., 1990, 15, 265–27268.
41 J. Li, J. S. Cisar, C. Zhou, B. Vera, H. Williams, 68 S. C. Petitto and M. A. Langell, J. Vac. Sci. Technol., A, 2004,
´
A. D. Rodrıguez, B. F. Cravatt and D. Romo, Nat. Chem.,
22, 1690.
2013, 5, 510–517.
69 L. Armelao, Surf. Sci. Spect., 2001, 8, 14.
Chem. Sci.
This journal is © The Royal Society of Chemistry 2018